The present invention relates to a method for fabricating a semiconductor device.
A conventional semiconductor device having a p-n junction is manufactured in the manner as shown in FIG. 1. Referring to FIG. 1, a boat 2 with a number of n-type semiconductor substrates 1 mounted thereon is housed in a diffusion envelope 3. A diffusion source 4 of Ga or Ga-Ge is also housed in the diffusion envelope 3 to perform the closed capsule diffusion and to form a Ga-doped p-type region in each semiconductor substrate 1.
However, with this method for fabricating the semiconductor device, the amount of the impurity (Ga) to be doped in the semiconductor substrate 1 must be controlled based on the weight of the diffusion source 4. For this reason, it is difficult to obtain p-type regions of desired sheet resistivity and junction depth. Variations in the properties of the p-type regions are also great from one lot to another of the diffusion furnace 3. Another method is also proposed in Japanese Pat. No. 763613 wherein an impurity region is formed by implanting, by the ion implantation method, an impurity into the semiconductor substrate not under a closed condition but in an open atmosphere. However, the inventors have determined that when the impurity is gallium, the implanted gallium ions are diffused to the outside from the semiconductor substrate and a protective film formed thereover, so that the formation of the desired impurity region has been difficult.